1. Field of Invention
The present invention is in the field of electronic circuits and, more particularly, is directed to a switch circuit and method of operating same.
2. Discussion of Related Art
When a switch makes or breaks a circuit connecting a voltage source to a load, there is power loss that occurs in the switch during the transition. FIG. 1 illustrates a basic circuit diagram of a voltage source 100 connected to a load 110 via a switch 120 and diode 130. Those skilled in the art will appreciate that although the diode 130 is illustrated separate from the switch 120, the diode 130 may be integrated with and a part of the switch 120. When the switch 120 is opened or turned off (from the closed/on position), during the transition period from on to off, the current in the switch falls, and the voltage across the switch rises, as shown in FIG. 2A. FIG. 2A illustrates a graph of the current (trace 210) and voltage (trace 220) in the switch (with units amps and volts, respectively, on the vertical axis) as a function of time (in microseconds on the horizontal axis). During the on-off transition, there is a period during which both current and voltage are present in the switch, referred to as the period of overlap, as can be seen in FIG. 2A. During this period of overlap, power loss in the switch 120 can be observed, as shown in FIG. 2B. In the illustrated example, for a voltage source operating at approximately 100 Volts (V) and 10 Amps (A), as shown in FIG. 2A, the power loss in the switch 120 is approximately 250 Watts (W), as shown in FIG. 2B. A similar loss is experienced during turn-on of the switch 120, as illustrated in FIG. 2C, during the period of overlap illustrated in FIG. 2D.
This problem may be even more pronounced in the case where the switch 120 connects the voltage source 100 to the load 110 via a current source 140, as shown in FIG. 3. This is the case in many power electronics applications. FIG. 4A illustrates a graph of switch current (trace 410) and voltage (trace 420) as a function of time for the circuit of FIG. 3. During the turn-off transition, the current 410 in the switch 120 falls, and the voltage 420 across the switch 120 rises, as shown in FIG. 4A. Power loss is experienced in the switch 120 during the period of overlap when current and voltage are both present in the switch, as shown in FIG. 4B. As can be seen from a comparison of FIGS. 2B and 4B, the power loss is greater (about 1 kilowatt (kW) versus 250 W) for the circuit of FIG. 3. During turn-on, the voltage 420 across the switch drops and the current 410 rises, as shown in FIG. 4C, and a similar power loss is experienced during the transition, as shown in FIG. 4D.